1. Field of the Invention
The present invention belongs to the technical field of an active matrix driven electro-optical device and a method for manufacturing the same, and more particularly, to an electro-optical device, which has storage capacitor electrodes for adding storage capacitance to pixel electrodes and which also has a conductive layer designated as a barrier layer for allowing favorable electrical conductance between a pixel electrode and a pixel switching thin film transistor (hereunder sometimes referred to as an TFT).
2. Description of Related Art
In a conventional active matrix TFT-driven electro-optical device, many scanning lines arranged along the columns of pixel electrodes, data lines arranged along the rows of pixel electrodes, and TFTs respectively corresponding to and disposed at intersections of the scanning and data lines are provided on a TFT array substrate. Each of the TFTs has a gate electrode connected to the scanning line, and also has a semiconductor layer, whose source and drain regions are respectively connected to the data line and the pixel electrode. Incidentally, especially, each of the pixel electrodes is connected to the drain region of the semiconductor layer of a corresponding TFT through a contact hole bored in an interlayer insulating film, because the pixel electrodes are provided on various kinds of layers of the TFTs and on the interlayer insulating film for insulating the pixel electrodes from one another. Further, when a scanning signal is supplied to the gate electrode of the TFT through the scanning line, the TFT is turned on. Moreover, an image signal supplied to the source region of the semiconductor layer through the data line is fed to the pixel electrode through the source-drain path of the TFT. Such supply of the image signal is supplied to each of the pixel electrodes through a corresponding one of the TFTs only for an extremely short time. Thus, generally, a storage capacitor is formed in each of the pixel electrodes in parallel with a liquid crystal capacitor so as to hold the voltage of an image signal, which is supplied through the TFT turned on for an extremely short time, for a time that is far longer than the extremely short time. On the other hand, in this kind of an electro-optical device, the source and drain regions and the channel region, which is formed between the source and drain regions, of each of the pixel switching TFTs are constituted by the semiconductor layers formed on the TFT array substrate. The pixel electrodes need to be connected to the drain regions of the semiconductor layers through a laminated structure containing wirings, such as the scanning lines, the storage capacitor lines, and the data lines, and a plurality of interlayer insulating films for electrically insulating these wirings. Incidentally, especially, in the case of staggered type or coplanar type polysilicon TFTs, each having a top gate structure in which a gate electrode is provided on a semiconductor layer, the interlayer distance from the semiconductor layer of the laminated structure to the pixel electrode is long, for example, about 1000 nm or more. It is, thus, difficult to form a contact hole for electrically connecting both the semiconductor layer and the pixel electrode. More specifically, it is extremely difficult to form such a deep hole only by dry etching, because of etching accuracy degradation that is caused by increasing the depth of a portion, on which the etching is performed, and that results in possibility of penetrating a target semiconductor layer to thereby form a hole. Thus, a combination of dry etching and wet etching is performed. However, this wet etching results in an increase in the diameter of the contact hole. Consequently, it is difficult to lay out necessary amounts of wires and electrodes in a limited region on the substrate.
Hence, recently, the following technique has been developed. That is, when the electrical connection between the data line and the source region is provided by making a contact hole, which is led to the source region of the semiconductor layer, in the interlayer insulating film formed on the scanning line, a relaying conductive layer designated as a barrier layer is formed from the same layer as that constituting the data line on the interlayer insulating film by forming a contact hole led to the drain region of the semiconductor layer. Then, a contact hole guided to this barrier layer from the pixel electrode is formed in the interlayer insulating film formed on the data line and this barrier layer. Such a configuration, in which the electrical connection from the pixel electrode to the drain region is provided via the barrier layer constituted by the same layer as that of constituting the data line, a contact hole forming step is facilitated, as compared with the case of forming a contact hole in such a way as to be led from the pixel electrode directly to the semiconductor layer. Moreover, the diameter of the contact hole led to the drain region via the barrier layer is smaller than that of the contact hole led directly to the semiconductor layer.
In the case of such a conventional electro-optical device, there is a keen ordinary demand for enhancing the picture quality of a displayed image. It is extremely important in meeting such a demand to realize a highly fine image display region or a fine pixel pitch, and to attain a high pixel aperture ratio (that is, to enhance the ratio of a pixel aperture region, which transmits display light, to a non-pixel-aperture region, which does not transmit display light, corresponding to each pixel).
However, this kind of conventional electro-optical device has a drawback in that the pixel aperture ratio is low at a highly fine pixel pitch because there is an essential limit to the degree of fineness of each of the electrode size, wire width, and contact-hole diameter, which results from fabrication techniques, and that thus, the proportion of the area of a region which contains such wires and electrodes relative to the area of the image display region increases.
Furthermore, when the degree of fineness of the pixel pitch is enhanced in this manner, it is difficult to realize the aforementioned storage capacitor which has sufficient storage capacitance and is incorporated into the limited region on the substrate. Incidentally, particularly, according to the aforementioned technique using the barrier layer, the barrier layer is constituted by conductive film, such as Al (aluminum) film, which is the same as the conductive film constituting the data line. Thus, the degree of flexibility of forming a contact hole is low owing to the position and material of the barrier layer. Moreover, it is extremely difficult to use the barrier layer for purposes other than that of performing the relaying function. Particularly, it is impossible to simplify the configuration of the device and to enhance efficiency of a manufacturing process by making the most of each of the layers of the fine laminated structure. Additionally, according to this technique, a chemical reaction is caused by bringing the Al film constituting the barrier layer in contact with an ITO (Indium Tin Oxide) film constituting the pixel electrode. As a result, the readily ionizable Al film is subject to corrosion. This impairs the electrical connection between the barrier layer and the pixel electrode. Thus, it is necessary to use a high melting point metallic film, for instance, Ti (titanium) film, as a second barrier layer, so as to provide the favorable electrical connection between the ITO film and the second barrier layer. Consequently, this conventional electro-optical device has a drawback in that the structure of the layers and the process of fabricating the layers are complexed.
The present invention is accomplished in view of the aforementioned drawbacks. A problem to be solved by the present invention is to provide an electro-optical device, which can favorably electrically relay between the pixel electrode and the thin film transistor and increase the storage capacitance by using a relatively simple configuration even when a fine pixel pitch is employed, and which also can display a high-picture-quality image, and to provide a method for manufacturing the electro-optical device.
To solve the aforementioned problems, according to the present invention, there is provided a first electro-optical device, which may consist of a substrate that has a plurality of scanning lines, a plurality of data lines, thin film transistors connected to the plurality of scanning lines and the plurality of data lines, and pixel electrodes and storage capacitors connected to the thin film transistors.
This first electro-optical device may further consist of a first interlayer insulating film formed above an electrode corresponding to one of the plurality of scanning lines and the plurality of storage capacitors, a conductive layer formed above the first interlayer insulating film, and a second interlayer insulating film formed above the conductive layer. The plurality of data lines are formed on the second interlayer insulating film.
According to the first electro-optical device of the present invention, electrodes of one of a group of scanning lines and a group of storage capacitors, a first interlayer insulating film, a conductive layer, a second interlayer insulating film, and data lines are formed on the substrate in this order. Therefore, the electrically conductive layer interposed between the scanning line and the data line can be utilized for various purposes. The semiconductor layer and the pixel electrode can be electrically connected through the conductive layer to each other by connecting, for instance, first, the conductive layer and the semiconductor layer through the first contact hole, and moreover, connecting the conductive layer and the pixel electrode through the second contact hole. Alternatively, storage capacitance can be imparted to the pixel electrodes by using a part of the conductive layer as a storage capacitor electrode facing a part of the semiconductor layer and the other of the storage capacitor electrodes through the dielectric film. Alternatively, at least a part of the opened region of the pixel can be defined with a conductive layer by forming the conductive layer from a light shielding film. Additionally, the data lines, the scanning lines, and other wirings other than the storage capacitor lines for one of the storage capacitor electrodes can be constituted by conductive layers. Further, the redundant wires of the data lines, the scanning lines, and the storage capacitor lines can be formed from conductive layers.
According to an embodiment of the first electro-optical device of the present invention, the substrate is further provided with a third interlayer insulating film formed on the data lines. The pixel electrodes are formed on the third interlayer insulating film and electrically connected to the conductive layer through the contact holes formed in the second and third insulating films. The conductive layer is electrically connected to the semiconductor layer.
In such a configuration, the pixel electrodes are formed on the data lines via the third interlayer insulating film. The pixel electrodes are electrically connected to the conductive layer through the contact holes formed in the second and third insulating films. The conductive layer is connected to the semiconductor layer. Thus, there is provided the configuration, in which the semiconductor layer and the pixel electrodes are electrically connected to one another through the conductive layer.
To achieve the foregoing object, there is provided a second electro-optical device, which may consist of a substrate that has a plurality of scanning lines, a plurality of data lines, thin film transistors connected to the plurality of scanning lines and the plurality of data lines, pixel electrodes connected to the thin film transistors, semiconductor layers constituting of source regions, drain regions and first storage capacitor electrodes of the thin film transistors, an insulating thin film formed on each of the semiconductor layers, a gate electrode of each of the thin film transistors, which is formed on the insulating thin film and constituted by a part of the scanning lines, a second storage capacitor electrode of each of the storage capacitors formed on the insulating thin film, a first interlayer insulating film formed on the scanning lines and the second storage capacitor electrodes, a conductive layer formed on the first interlayer insulating film, and a second interlayer insulating film formed on the conductive layer. The data lines are formed on the second interlayer insulating film and electrically connected to the source region of the semiconductor layer through contact holes formed in the first and second interlayer insulating films.
According to the second electro-optical device of the present invention, the scanning lines, the second storage capacitor electrodes, the first interlayer insulating film, the conductive layer, the second interlayer insulating film, and the data lines are formed on the substrate in this order. The pixel electrodes are formed further above. Further, the data lines are electrically connected to the source region of the semiconductor layer through the contact holes formed in the first and second interlayer insulating films. In addition, the source and drain regions thereof are constituted by a part of the semiconductor layer. The gate insulating film of the thin film transistor is constituted by a part of the insulating film. Moreover, the gate electrode of the thin film transistor, which is formed from a part of the scanning lines, is formed on the insulating thin film. On the other hand, the first storage capacitor electrode is formed from a part of the semiconductor layer. A dielectric film of the storage capacitor is formed from a part of the insulating thin film. Furthermore, the second storage capacitor electrode constituted by a part of the storage capacitor lines is formed on the insulating film. Thus, the thin film transistors are disposed under the scanning lines. In parallel with this, the storage capacitors are placed under the second storage capacitor electrode. Therefore, with a configuration in which such storage capacitors and the thin film transistors are placed side by side, the conductive layer between the scanning lines and the data lines can be utilized for various purposes. For example, first, a part of the conductive layer is used as a third storage capacitor electrode facing the second storage capacitor electrode through the first interlayer insulating film. Namely, the first interlayer insulating film is used at this place as a dielectric film of the storage capacitor, so that the a part of the conductive layer and the second storage capacitor electrode are disposed in such a manner as to be opposed to each other. Thus, additional storage capacitance can be added to the pixel electrodes (in addition to storage capacitor obtained from the first and second storage capacitor electrodes). Alternatively, similarly as in the case of the aforementioned first electro-optical device of the present invention, the semiconductor layer can be electrically connected to the pixel electrodes through the conductive layer. Alternatively, at least a part of the opened region of the pixel can be defined with a conductive layer. Moreover, the data lines, the scanning lines, and other wirings other than the storage capacitor lines for one of the storage capacitor electrodes can be constituted by conductive layers. Further, the redundant wires of the data lines, the scanning lines, and the storage capacitor lines can be formed from conductive layers.
According to an embodiment of the second electro-optical device of the present invention, the conductive layer is electrically connected to the drain region of the semiconductor layer through the contact holes formed in the first interlayer insulating film and the insulating thin film.
In such a configuration, the data lines are electrically connected to the source region of the semiconductor layer through the contact holes formed in the insulating thin film and the first and second interlayer insulating films. The conductive layer is electrically connected to the drain region of the semiconductor layer through the contact holes formed in the first interlayer insulating film and the insulating thin film. Thus, the conductive layer can easily be used as the storage capacitor electrode connected to the pixel electrode. Simultaneously, the pixel electrodes and the drain region of the semiconductor layer can be easily and electrically connected to each other through the conductive layer.
According to another embodiment of the second electro-optical device of the present invention, the substrate may further consist of the third interlayer insulating film formed on the data lines. Moreover, the pixel electrodes are formed on the third interlayer insulating film, and electrically connected to the conductive layer through contact holes formed in the second and third interlayer insulating films.
In such a configuration, the pixel electrodes are formed above the data lines through the third interlayer insulating film. The pixel electrodes are electrically connected to the conductive layers via the contact holes formed in the second and third insulating films. Thus, the pixel electrodes and the drain region can be easily and electrically connected to each other through the conductive layer.
To achieve the foregoing object, according to the present invention, there is provided a third electro-optical device, which may consist of a plurality of pixel electrodes and a plurality of thin film transistors, which are arranged in a matrix on a substrate, scanning lines and data lines, connected to the thin film transistors via the interlayer insulating films and three-dimensionally intersecting with one another, a conductive layer, which is interposed between the semiconductor layer of the thin film transistor and the pixel electrode and electrically connected to the drain region of the semiconductor layer through a first contact hole and electrically connected to said pixel electrode through a second contact hole, a first dielectric film interposed between a first storage capacitor electrode, which is constituted by the same film as a film of a semiconductor portion constituting the drain region, and a second storage capacitor electrode disposed on said first storage capacitor electrode, and a second dielectric film interposed between the second storage capacitor electrode and a third storage capacitor electrode, which is constituted by a part of the conductive layers.
According to the third electro-optical device of the present invention, in the substrate, the plurality of scanning lines and the plurality of data lines three-dimensionally intersect with one another via the interlayer insulating film. The second storage capacitor electrodes for adding the storage capacitor to the plurality of pixel electrodes are provided therein separately therefrom. Further, the conductive layer is interposed between the semiconductor layer and the pixel electrode. On one hand, the conductive layer is electrically connected to the drain region of the semiconductor layer through the first contact hole. On the other hand, the conductive layer is electrically connected to the pixel electrode through the second contact hole. Thus, as compared with the case that only one contact hole is formed between the pixel electrode and the drain region, the diameter of contact holes can be reduced to a small value. That is, the deeper the formed contact hole, the lower the etching accuracy. Therefore, to prevent the contact hole from penetrating the thin semiconductor layer, the process of forming the hole has to be adapted so that a dry etching operation, by which the diameter of the hole can be decreased, is stopped halfway, and that finally, a wet etching operation is performed until the hole reaches the semiconductor layer. Therefore, the diameter of the contact holes has to be increased as a result of performing the non-directional wet etching operation. In contrast, according to the present invention, it is sufficient to connect the pixel electrode and the drain region of the semiconductor layer by the two series-connected first and second contact holes. Thus, the contact holes can be formed by dry etching. Alternatively, at least the length of a part of each of these holes which is dug by wet etching can be decreased. Consequently, the diameter of each of the holes can be reduced to a small value. Thus, dents and uneven portions formed in the surface portion of the conductive layer are small in the first contact hole. This expedites enhancement of the flatness of this pixel electrode portions. Furthermore, dents and uneven portions formed in the surface portion of the conductive layer are small in the second contact hole. This expedites enhancement of the flatness of this pixel electrode portions. As a result, this reduces poor conditions, such as disclination of electro-optical materials, such as liquid crystals, owing to dents and uneven portions formed in the surface parts of the pixel electrodes.
Furthermore, the first dielectric film is interposed between the first storage capacitor electrode constituted by a semiconductor layer portion constituting the drain region of the semiconductor layer, and the second storage capacitor electrode placed on the first storage capacitor electrode. These three elements allow the capacitance of the first storage capacitor electrode to be imparted to the pixel electrode that is connected to the drain region of the semiconductor layer. In addition, the second dielectric film is interposed between the second storage capacitor electrode and the third storage capacitor electrode constituted by a part of the conductive layer. Hence, these three elements allow the capacitance of the second storage capacitor electrode to be imparted to the pixel electrode. Consequently, the first and second storage capacitors are formed above and under the conductive layer in such a way as to be in parallel with one another. In this manner, the three-dimensional arrangement of the storage capacitors is realized in a limited region of the substrate. Incidentally, note that each of the first and second dielectric films is constituted by a dielectric film or layer that differs from the second interlayer insulating film between the scanning lines and the data lines, which three-dimensionally intersect with one another. Thus, the thickness of the first and second dielectric films can be reduced to a technical limit, regardless of the thickness of the second interlayer insulating film required to have a certain thickness so as to suppress parasitic capacitance between the scanning lines and the data lines, which would result in occurrence of flicker and cause a voltage drop of an image signal. Assuming that the barrier layer is used as one of the storage capacitor electrodes and the interlayer insulating film between the data lines and the scanning lines is used as the dielectric film in the aforementioned prior art device, in which this barrier layer (corresponding to the conductive layer of the present invention) is formed from the same conductive layer as constituting the data lines, this dielectric film should have a thickness of about 800 nm so as to eliminate the influence of the parasitic capacitance between the data lines and the scanning lines. Thus, it is essentially difficult to construct the storage capacitor of large capacitance by using the barrier layer. In contrast with this, the present invention can extremely efficiently increase the capacitance of the storage capacitors, which is inversely proportional to the thickness of a dielectric film, by using the dielectric film which can be formed in such a way as to have a small thickness.
Furthermore, according to the present invention, the diameter of the first contact hole can be decreased still more by forming the dielectric film in such a manner as to be small in thickness. The depth of the dents and the degree of the flatness of the uneven parts formed on the conductive layer can be reduced to a smaller value in the aforementioned first contact hole. This expedites the increase in the degree of the flatness of the surfaces of the pixel electrodes disposed above the conductive layer. Consequently, the poor conditions of the electro-optical material which are due to the dents and the uneven potions formed in the pixel electrodes are alleviated. Finally, this realizes an image display whose picture quality is enhanced still more.
Incidentally, in the case that the conductive layer and the second dielectric film are formed by attaching importance to the light shielding function of the conductive layer and the layout of the contact holes in place of or in addition to the storage capacitor adding function in this device of the present invention in such a way as to reach the scanning lines, it is sufficient to form the second dielectric film in such a manner as to be thick to the extent that the parasitic capacitance between the conductive layer and the scanning line is negligible. Therefore, in such a case, it is difficult to increase the capacitance of the storage capacitors when the thickness of the second dielectric film is reduced to the technical limit as described above. However, when sufficient storage capacitor is added to the device in view of the specifications of the device, there is no necessity for reducing the thickness of the second dielectric film further. It is advantageous for the entire electro-optical device to be constructed in such a manner as to expedite enhancement of the additional functions, such as the light shielding function of the conductive layer. In short, in view of the practical individual specifications of the device, it is sufficient to set the planar layout of the conductive layer and the thickness of the second dielectric layer so that the conductive layer fully achieve the essential functions, such as the relaying function and the function of adding the necessary storage capacitance, and the additional functions, such as the light shielding function.
According to an embodiment of the third electro-optical device of the present invention, the first and second storage capacitor electrodes at least partly overlap with each other through the first dielectric film in a planar view. Further, the second and third storage capacitor electrodes at least partly overlap with each other through the second dielectric film in a planar view.
With such a configuration, the first and third storage capacitor electrodes are respectively formed above and under the second storage capacitor electrode. Thus, the three-dimensional arrangement of the storage capacitor electrodes is realized on such a limited region of the substrate.
According to an embodiment of the third electro-optical device of the present invention, the first dielectric film and the insulating thin film are constituted by the same film. Further, the scanning lines and the second storage capacitor electrode are constituted by the same film. Moreover, the second interlayer insulating film is formed on the scanning lines and the conductive layer.
With this configuration, the first dielectric film and the insulating film of the thin film transistor are constituted by the same film, so that these insulating films can be formed in the same process. The scanning lines and the second storage capacitor electrode are constituted by the same film, so that these conductive films can be formed in the same process. Further, the second interlayer insulating film is formed on the scanning lines and the conductive layer. Moreover, the data lines are formed thereon. Therefore, the storage capacitance can be increased by forming the first and second dielectric films in such a manner as to have a small thickness. Simultaneously with this, the parasitic capacitance between the scanning lines and the data lines can be decreased by forming the second interlayer insulating film in such a way as to be relatively large in thickness. Consequently, a high-picture quality image display can be realized by using such a relatively simple configuration.
According to another embodiment of the third electro-optical device of the present invention, the first and second interlayer insulating films are constituted by the same film.
With this configuration, the first and second interlayer insulating films can be formed in the same process. It is advantageous to the device in that the number of steps of the manufacturing process is not increased.
According to another embodiment of the first, second or third electro-optical device of the present invention, the conductive layer is constituted by a conductive light shielding film.
With this configuration, the aperture region of each of the pixels can be defined at least partly by the conductive layer that is constituted by the conductive light shielding film. Such a configuration, in which a part of or all of a built-in light shielding film (that is, a conductive layer constituted by a light shielding film) is provided on the substrate (normally TFT array substrate) in place of a light shielding film formed on the other substrate (usually, the opposing substrate), is extremely advantageous in that the positional deviation between a substrate and an opposing substrate in the manufacturing process does not deteriorate the pixel aperture ratio.
In the case of this embodiment, in which the conductive layer is constituted by the light shielding film, it is preferable that the conductive layer be formed so that the projections of the conductive layer on the substrate extends between adjoining data lines along the scanning lines and in an island corresponding to each of the pixel electrodes.
With this configuration, in which the conductive layer is formed in island, the influence of stress of the film constituting the conductive layer can be reduced. Moreover, part or all of a side which extends along the scanning lines of the pixel aperture region can be defined by the conductive layer. Especially, in the case that the influence of the parasitic capacitance between the scanning line and the conductive layer cannot be neglected from the viewpoint of the practical design of the circuit of the device, it is preferable that the side which extends along the scanning lines of the pixel aperture region at the side, at which the storage capacitor lines adjoin the pixel electrodes, is defined by the conductive layer without providing the conductive layer on the scanning lines.
In the case of this embodiment, in which the island-like light shielding film is provided as the conductive layer, the adjoining data lines and the conductive layer may be formed so that these lines and the layer at least partly overlap with each other in a planar view.
With this configuration, there is no gap through which light penetrates between the end portion of the island-like conductive layer and the edge of each of the data lines. That is, the edge portions of the data lines coincide with or slightly overlap with the end portion of the conductive layer. Thus, this embodiment can prevent an occurrence of a poor-quality display, such as light leakage, in this portion.
In the case of this embodiment, in which the aforementioned conductive layer is constituted by the light shielding film, the conductive layer and the scanning lines overlap with each other in a planar view.
With this configuration, the side, which extends along the scanning lines, of the pixel aperture region may be defined by the conductive layer constituted by the light shielding film that is adapted to at least partly cover both the groups of the scanning lines and the storage capacitor lines.
In the case of the embodiment, in which the aforementioned conductive layer is constituted by the light shielding film, the conductive layer may contain high-melting-point metal.
With this configuration, the conductive layer can be prevented from being broken or melted by a high temperature treatment to be performed after the conductive layer constituted by the light shielding film is formed. For example, the light shielding film is constituted by a metallic simple substance, an alloy, or a metallic silicide, which contains at least one of Ti, Cr (chrome), W (tungsten), Ta (tantalum), Mo (molybdenum), and Pb (lead) that are opaque high-melting-point metals.
In the case of another embodiment of the first, second, or third electro-optical device of the present invention, the conductive layer is constituted by an electrically conductive polysilicon film.
With this configuration, the conductive layer constituted by the conductive polysilicon film can fully achieve the storage-capacitance increasing function and the relaying function, though this layer does not fully serve as a light shielding film. In this case, especially, stress due to heat or the like hardly occurs between this film and the interlayer insulating film. Thus, this device is advantageous in that the generation of cracks in and around the conductive layer is avoided.
In the case of another embodiment of the first, second, or third electro-optical device of the present invention, the conductive layer is constituted by a laminated layer film consisting of two or more layers made of conductive polysilicon film and high-melting-point metal.
With this configuration, the conductive layer constituted by the conductive polysilicon film can fully achieve the storage-capacitance increasing function and the relaying function, though this layer does not fully serve as the light shielding film. Further, when the semiconductor layer is electrically connected to the conductive polysilicon film, if the semiconductor layer is formed from the same polysilicon film, the contact resistance can be considerably lowered. Moreover, if a high-melting-point metal layer is stacked on such a conductive polysilicon film, the conductive layer fully serves as the light shielding film. Furthermore, the resistance thereof can be lowered.
In the case of another embodiment of the first, second, or third electro-optical device of the present invention, the substrate further has a light shielding film provided in an area at which the light shielding film covers the channel region of said semiconductor layer in a planar view.
With this configuration, the light shielding film provided at a side which is nearer to the substrate than the thin film transistor that is, provided under the thin film transistor, can prevent return light from entering the channel region and LDD (lightly doped drain) region of the thin film transistor, and can prevent the characteristics of the thin film transistor from being changed and deteriorated by the generation of a photoelectric current. Moreover, all or part of the pixel aperture region can be defined by this light shielding film.
In the case of the embodiment having this light shielding film, the light shielding film may extend under the scanning lines and may be connected to a constant potential source.
With this configuration, the characteristics of the thin film transistor provided above the light shielding film via an underlying insulating film are prevented from being changed and deteriorated due to variation in the electric potential of the light shielding film.
Alternatively, in the case of the embodiment including this fight shielding film, the light shielding film may be electrically connected to the second storage capacitor electrode through a contact hole formed in an underlying insulating film interposed between the light shielding film and the semiconductor layer.
With this configuration, the electric potential at the second storage capacitor electrode can be made to be equal to that at the light shielding film. If the electric potential at one of the second storage capacitor electrode and the light shielding film is set at a predetermined value, the electric potential at the other of the second storage capacitor electrode and the light shielding film can be set at the predetermined value. At that time, if the light shielding film is a storage capacitor line, the second storage capacitor electrode is connected to the capacitor line, so that constant electric potential can be applied to said second storage capacitor electrode. Consequently, the negative influence of electric potential fluctuation at the second storage capacitor electrode and the light shielding film can be reduced.
According to another embodiment of the third electro-optical device of the present invention, the second storage capacitor electrode is extended and serves as the capacitor line.
With this configuration, the electric potential at the capacitor line can be maintained at a constant level. Thus, the electric potential at the second storage capacitor electrode can be stabilized. Further, at that time, the capacitor lines and the scanning lines can be formed from the same film.
According to another embodiment of the third electro-optical device of the present invention, the capacitor line is electrically connected to the light shielding film through the underlying insulating film.
With this configuration, the electric potential at the capacitor lines can be made to be equal to that at the light shielding film. If the electric potential at one of the capacitor lines and the light shielding film is set at a predetermined value, the electric potential at the other of the capacitor lines and the light shielding film can be set at the predetermined value. Consequently, the negative influence of electric potential fluctuation at the capacitor lines and the light shielding film can be reduced. Further, the wire constituted by the light shielding film and the capacitor lines can be mutually made to serve as redundant wires.
According to another embodiment of the third electro-optical device of the present invention, the conductive layer and the light shielding film may be disposed so that the conductive layer at least partly overlaps with the light shielding film in a planar view.
With this configuration, the conductive layer and the light shielding film are formed in such a way as to sandwich the channel region of the semiconductor layer therebetween. Thus, light can be prevented from entering the channel region from the substrate side thereof and the other side. Consequently, the characteristics of the thin film transistors can be prevented from being changed and deteriorated. Moreover, this can prevent an occurrence of a crosstalk, a reduction in the contrast ratio, and deterioration in a flicker level.
According to another embodiment of the first, second, or third electro-optical device of the present invention, the underlying insulating film is provided between the substrate and each of the thin film transistors. Moreover, the third interlayer insulating film is provided on the data lines and under the pixel electrodes. At least one of the substrate, the underlying insulating film, the second interlayer insulating film, and the third interlayer insulating film is formed in such a way as to be partly dented in at least one of regions respectively corresponding to the thin film transistors, the scanning lines, the data lines, and the storage capacitors. Thus, the foundation surface of the pixel electrodes is formed in such a manner as to be almost flat.
With this configuration, at least one of the substrate and a plurality of interlayer insulating films is formed in such a way as to be partly dented in at least one of regions corresponding to the thin film transistors, the scanning lines, the data lines, and the storage capacitors. Thus, the difference between regions, in which the thin film transistors, the scanning lines, and the storage capacitors are formed in such a way as to overlap with the data lines, and other regions can be reduced. In this way, the bottom surfaces of the pixel electrodes are made to be almost flat. Consequently, the degree of the flatness of the surface of each of the pixel electrodes can be increased still more. Thus, this reduces poor conditions, such as disclination, of electro-optical materials, such as liquid crystals, owing to dents and uneven portions formed in the surface parts of the pixel electrodes. Finally, a high-picture-quality image display can be achieved.
According to another embodiment of the third electro-optical device of the present invention, the first contact hole and the second contact hole are formed at different places on the surface of the substrate.
Small dents and uneven portions are formed in the conductive layer corresponding to the place on the surface thereof, in which the first contact hole is formed. Thus, when the second contact hole is further formed just above this place, it is difficult to provide favorable electrical connection therebetween. Therefore, if the positions on the surface respectively corresponding to these holes are slightly differed from each other, it is expected that the favorable electric connection therebetween is provided.
According to another embodiment of the first, second, or third electro-optical device of the present invention, the thickness of the conductive layer ranges from 50 nm to 500 nm.
With this configuration, there is almost or entirely no negative effect (for instance, poor alignment of the liquid crystals) due to the difference in height between the surfaces of the pixel electrodes, which is caused by the presence of the conductive layer, because the thickness of the conductive layer ranges from 50 nm to 500 nm. Or else, the negative influence of such difference therebetween can be eliminated by flattening or leveling the interlayer insulating film placed above the conductive layer. Further, various advantageous effects can be obtained by alleviating the negative influence of the conductive layer.
According to another embodiment of the second electro-optical device of the present invention, the thickness of the first interlayer insulating film ranges from 10 nm to 200 nm.
With this configuration, the first interlayer insulating film is formed as a relatively thin insulating film, because the thickness thereof ranges from 10 nm to 200 nm. Therefore, if an additional storage capacitor is constructed, as described above, by utilizing this first interlayer insulating film as the dielectric film so that the first and second storage capacitor electrodes and the conductive layer are placed in such a way as to be opposed to each other through the first interlayer insulating film, the storage capacitor having large capacitance can be obtained according to the thickness thereof.
According to anther embodiment of the third electro-optical device of the present invention, the thickness of the second dielectric film ranges from 10 nm to 200 nm.
With this configuration, the second dielectric film is a relatively thin insulating film because the thickness of the second dielectric film ranges from 10 nm to 200 nm. Thus, the storage capacitor obtained by placing the second and third storage capacitor electrodes in such a manner as to be opposed to each other through the second dielectric film is large according to the thickness thereof.
According to an embodiment in which the conductive layer is constituted by the light shielding film, the conductive layer may be formed in such a fashion as to define at least a part of the pixel aperture region.
With this configuration, the pixel aperture region can be defined by the conductive layer singly, or together with the data lines and the light shielding film formed on the other substrate. Especially, if the aperture region is defined without forming the light shielding film on the other substrate, the number of steps of the manufacturing process can be decreased. Moreover, a decrease or variation in the pixel aperture ratio, which would be caused by alignment deviation between a pair of the substrates, can be prevented. This is advantageous for the electro-optical device.
To achieve the foregoing object, according to the present invention, there is provided a method for manufacturing an electro-optical device, which has a plurality of scanning lines, a plurality of data lines, thin film transistors placed correspondingly to intersections between the scanning lines and the data lines, and pixel electrodes and storage capacitors connected to the thin film transistors. This method may consist of the steps of forming a source region, a channel region, and a drain region of each of the thin film transistors, and a semiconductor layer constituting a first storage capacitor electrode corresponding to one of the storage capacitors on a substrate, forming an insulating thin film on the semiconductor layer, forming the scanning lines and a second storage capacitor electrode of one of the storage capacitors on the insulating thin film, forming a first interlayer insulating film on the second storage capacitor electrode, forming a first contact hole in the gate insulating film and the first interlayer insulating film, forming a conductive layer on the first interlayer insulating film so that the conductive layer is electrically connected to the semiconductor layer through the first contact hole, forming a second interlayer insulating film on the conductive layer, forming the data lines on the second interlayer insulating film, forming a third interlayer insulating film on the data lines, forming a second contact hole in the second and third interlayer insulating films, and forming the pixel electrodes in such a manner as to be electrically connected to the conductive layer through the second contact hole.
According to the method for manufacturing an electro-optical device of the present invention, the electro-optical device can be manufactured by performing a relatively simple process.
An embodiment of the method for manufacturing an electro-optical device of the present invention may further consist of the steps of: forming a light shielding film in a region facing the channel region of the substrate, and forming an underlying insulating film on the light shielding film. In the step of forming the semiconductor layer, the semiconductor layer is formed on the substrate insulating film.
With such constitution, an electro-optical device, in which the light shielding film is provided under the thin film transistors, can be manufactured by performing a process consisting of a relatively small number of steps, each of which are relatively simply achieved.
An embodiment of the method for manufacturing an electro-optical device of the present invention may further consist of the step of making at least one of the substrate, the underlying insulating film, the second interlayer insulating film, and the third interlayer insulating film to be dented in a part of at least one of regions respectively corresponding to the thin film transistors, the scanning lines, the data lines, and the storage capacitors.
According to such an embodiment, the bottom surface of each of the pixel electrodes can be flattened by forming making at least one of the substrate, the underlying insulating film, the second interlayer insulating film, and the third interlayer insulating film to be dented in a part of at least one of regions respectively corresponding to the thin film transistors, the scanning lines, the data lines, and the storage capacitors. Thus, poor conditions, such as disclination, can be alleviated. Such effects and other advantages will become apparent from the following description of embodiments of the present invention.